1. Field of the Invention
This invention relates to optical communication networks and more particularly relates to a system and method for increasing the channel capacity and total system throughput of a fiber-optic communication network utilizing three-dimensional spatial field.
2. Background Information
As data communication systems and networks consume more and more bandwidth, fiber-optics has emerged as a leading technology for metropolitan and long-haul data transmissions. Access techniques, adapted from electronics communication, such as Code Division Multiplexing (CDM), Frequency Division Multiplexing (FDM), and Time Division Multiplexing (TDM) have been used in fiber-optic systems and networks. For example, Wavelength Division Multiplexing (WDM) is essentially FDM in the optical domain. To further conserve the bandwidth of an optical network, a so-called Dense WDM (DWDM) standard has been proposed with the channel separation set at 0.8 nm in wavelength, or 100 GHz in frequency.
One area unique to optical communications has provided another dimension for capacity enhancement. This is the polarization of an optical signal. Lithium Niobate (LiNbO) phase modulators and polarization controllers, and Pockels cells have been used to implement polarization shift keying (POLSK). Other investigations have considered polarization of signals in different wavelength channels. One example is in U.S. Pat. No. 6,038,357 of Pan issued Mar. 14, 2000 that discloses a fiber-optic PDM/WDM system comprising a plurality of sets of laser sources maintained at fixed polarization states. Each state represents a different channel. The design disclosed in that patent accomplishes an increase in the number of channels at the expense of using multiple sets of laser sources. Another U.S. Pat. No. 6,025,944 of Mendez et al issued Feb. 15, 2000 discloses a clever but complex coding scheme to perform hybrid mixing of Wave Division Multiplexing (WDM) and Code Division Multiple Access (CDMA). The tradeoff in using a complex switching and coding method to improve channel capacity is unclear.
It is one object of the present invention to provide a system and method for increasing channel capacity and throughput of an optical communications network by a combination of Polarization Modulation (PM), Wavelength Division Multiplexing (WDM), and Time Division Multiplexing (TDM). Time division multiplexing increases the number of available channels while polarization modulation increases the throughput.
It is another object of the present invention to provide a system and method for increasing channel capacity and throughput by applying space-time modulation to guided optical communications.
Yet another object of the present invention is to provide a system and method of increasing channel capacity and throughput by direct modulation of optical sources.
Still another object of the present invention is to provide a system and method for increasing transmission distance by including signal amplification with optical amplifiers inserted in the optical transmission fiber.
Yet another object of the present invention is to provide a system and method for increasing channel capacity and throughput in which an optical wavelength cross-connect is inserted in an optical fiber transmission line to reuse wavelengths.
Still another object of the present invention for increasing channel capacity of an optical network in which temporal data streams from time division multiplexers are modulated on optical sources.
Still another object of the present invention is for increasing throughput of an optical network in which spatial data streams from time division multiplexers are modulated on outputs of optical sources by varying the polarization states of the optical field.
Yet another object of the present invention is to provide a system and method for increasing channel capacity and throughput which can be applied to conventional wavelength division multiplexing ring network.
Yet another object of the present invention is to provide a system and method for increasing channel capacity and throughput which can be applied to a conventional wavelength division multiplexing fiber-optic star coupled network of a plurality of wavelengths.
Still another object of the present invention is to provide a system and method for increasing channel capacity and throughput by application to a conventional wavelength division multiplexing fiber-optic data bus network operating with multiple wavelengths comprised of multiple Network Interface Units (NUI) communicating over an optical fiber network.